Ethernet communications provide high speed data communications over a communications link between communication nodes (or network devices) that are operating according to the IEEE 802.3 Ethernet standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types of communications medium that are appropriate. Powers over Ethernet (POE) communication systems, based on IEEE 802.3af, may provide power and data communications over a common communications link. More specifically, a power source device (e.g., power source equipment (PSE)) connected to the physical layer of the first node of the communications link provides DC power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously from PSE to PD over the same communications medium that high speed data is transmitted between PD and PSE. In this manner, a separate power cable may be avoided or unnecessary for the PD.
The PSE device may be a data switch, a computer, or other device, for example. A PSE may include one or more data ports (or Ethernet ports). Each port may include a transceiver to transmit and receive data over a data link or communications medium (e.g., one or more twisted pair wires, or Ethernet cable) that may be connected to a data port on another device or node. Herein, data ports and their corresponding links can be interchangeably referred to as data channels, communication links, data links, etc, for ease of discussion.
Typical PD devices that use POE to receive power may include a wide variety of devices, such as, for example, Internet Protocol (IP) phones (Voice over IP (VoIP) phones), wireless access points, personal computing devices, such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device. Each type of PD may have a different power requirement. For example, the power requirements of personal computing devices (e.g., laptops) are typically significantly higher than that of VoIP phones, wireless access points, and other limited purpose devices (e.g., print server). In addition, a personal computing device may change its power draw depending on its application load. Moreover, personal computing devices can power other devices such as USB devices or external drives, for example, which will affect total power draw.
A PSE device (e.g., a PSE switch) may typically have a POE power budget, which may indicate a maximum amount of power (e.g., 200 W) available to provide to one or more connected PDs (connected via one or more Ethernet ports). IEEE 802.3af allows a maximum length of 100 meters for an Ethernet cable or link between a PSE and PD. In allocating power to a PD, PSE devices typically assume that each PD is connected via a maximum length (100 m) cable. Although, in some cases, PDs may be connected to the PSE via shorter length links or cables. By assuming a 100 meter (or maximum length) link or cable for all connected PDs, this may cause a PSE to allocate to each PD a greater amount of power than is necessary. This may unnecessarily decrease the number of PDs that may be supported or the amount of power that is available for other PDs.